Radiography systems and methods are widely used, particularly for medical imaging and diagnosis. Radiography systems generally create two-dimensional projection images through a subject's body. A radiation source, such as an X-ray tube, irradiates the body from one side. A collimator, generally adjacent to the X-ray source, limits the angular extent of the X-ray beam, so that radiation impinging on the body is substantially confined to a cone-beam/fan-beam region (i.e., an X-ray projection volume) defining an image volume of the body. At least one detector on the opposite side of the body receives radiation transmitted through the body substantially in the projection volume. The attenuation of the radiation that has passed through the body is measured by processing electrical signals received from the detector.
Devices used in interventional procedures are becoming increasingly complex, which puts an increasing demand on X-ray image quality. A high resolution is desirable to visualize small details of the image. However, spatial resolution can be limited by the detector pixel size.
Un-sharpness is a loss of spatial resolution in a radiographic image. Geometric un-sharpness is caused by aspects of the geometry of the X-ray beam. Two factors related to geometric un-sharpness are the apparent focal spot size and the ratio between object-imager distance (OID) and source-imager distance (SID).
A focal spot is the point where the electron beam strikes a target within an X-ray tube. Fine focal spot sizes will minimize geometric un-sharpness and therefore, give more detailed images. However, it is often difficult to employ fine focal spot sizes due to the X-ray tube loading necessary in the exposure.
Geometric un-sharpness can be minimized by keeping the ratio SID:OID high. This can be accomplished by keeping the OID to a minimum, i.e. keeping the body portion being X-rayed as close to the detector as possible. Keeping the ratio SID:OID high can also be achieved by increasing the SID beyond a normal usage distance, such as a distance greater than 100-110 cm.
In current systems, the focal spot size can be large and therefore, can degrade the overall resolution. A high resolution detector with a smaller pixel size is more sensitive to the resolution degradation, due to a finite size of focal spots and magnification factors. Tube design limitations and X-ray output limitations are not conducive to using an actual point-size focal spot.
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as conventional art at the time of filing, are neither expressly nor implicitly admitted as conventional art against the present disclosure.